Novel hybrid materials for improved photovoltaic device efficiencies

原则上，光伏（PV）设备可以以可持续的方式满足我们所有的能源需求：地球表面每小时接收的光能足以为整个人口提供一年的电力。然而，目前传统光伏发电的资本支出太大，没有竞争力，而且它们的产量太小，不足以对我们的发电需求造成严重影响。因此，太阳能光伏发电（pv）占我们能源发电量的不到0.1%。传统的硅基光伏电池制造成本高，而且涉及能源密集型制造，而有机光伏电池可以使用大批量的卷对卷印刷技术进行加工，有望生产出大面积、廉价的柔性衬底光伏薄膜，原则上可用于覆盖窗户、墙壁和屋顶。这种设备已经被商业化生产，用于高移动性、低功耗的应用，比如包含柔性有机光伏设备的背包，为手机和类似产品充电。聚合物基pv的外部功率效率在10-15年的时间里从90年代中期的不足1%急剧增加到不足6%。其中一个最有前途的系统涉及两种分子材料P3HT（一种聚噻吩长链分子）和PCBM（一种功能化富勒烯）的混合物。这些材料的制备涉及到有限的偏析，导致在大约10纳米的长度尺度上的双连续结构，这样电子和空穴可以在两种材料之间的界面上相对有效地分离。P3HT/PCBM系统的效率受到P3HT相对较大的带隙的限制，使得在太阳光谱的红端光吸收效率低下。因此，新的高分子材料正在被开发，但通常是由公司申请专利，合成成本昂贵，具有较低的带隙，将吸收性能扩展到红色/红外线波长。我们正在开发一种替代方法，使用混合结构来增加局部电场并增强光学吸收。然后，这些混合材料将用于制造原型光伏设备，以评估能量转换（太阳能到电力）的效率。首先，我们希望开发效率大于6%的光伏设备，与市场领先者相比具有优势。这将允许进一步的资本投资，一旦效率达到9- 10%，就可以实现更大规模应用的长期目标。

In principle, photovoltaic (PV) devices could meet all our energy requirements in a sustainable way: the earth's surface receives enough light energy per hour to power the entire human population for one year. However, the current capital expense of conventional photovoltaics is too great to be competitive, and the volume in which they can be produced is much too small to make a serious dent in our electricity generating needs. As a consequence solar photovoltaics (PVs) account for < 0.1 % of our energy generation. Whereas conventional silicon-based PVs have high manufacturing costs and involve energy-intensive fabrication, organic PVs can be processed using high-volume roll-to-roll printing technology, promising large-area, cheap photovoltaic films of flexible backing material that could be used in principle to coat windows, walls and roofs. Such devices are already being produced commercially for high-mobility, low-power applications such as rucksacks comprising flexible organic PV devices to charge mobile phones and similar products. The external power efficiencies of polymer-based PVs have increased dramatically from sub-1% in the mid-90s to <6% in a period of 10-15 years. One of the most promising systems has involved a blend of two molecular materials P3HT (a polythiophene long-chained molecule) and PCBM (a functionalized fullerene). The preparation of these involves limited segregation that leads to a bicontinuous structure on the lengthscale of around 10 nm, such that electrons and holes can be separated relatively efficiently at an interface between the two materials. The efficiency of the P3HT/PCBM system is limited by the relatively large band-gap of P3HT, which renders the optical absorption inefficient at the red end of the solar spectrum. Consequently, new polymer materials are being developed, but are usually patented by companies and expensive to synthesise, that have lower band-gaps extending the absorption performance to red/infra-red wavelengths. We are developing an alternative approach using hybrid structures to increase the local electric field and to enhance the optical absorption. These hybrid materials will then be used to fabricate prototype photovoltaic devices allowing an assessment of the power conversion (solar-to-electricity) efficiencies. In the first instance, we hope to develop photovoltaic devices with efficiencies of greater than 6 %, comparing favourably with the market leaders. This will allow further capital investment to be sought with the long-term aim of larger scale applications being realised once efficiencies reach 9-10 %.